Diaphragm type gas meters, in which the volume of gas consumed is measured by the movement of one or more bellows, or diaphragms, are widely known and used for relatively low flows, such as domestic metering. The diaphragm is mechanically connected through a linkage to an index, or register, which accumulates the total volume of gas passed through the meter, usually measured in cubic feet. One of these meters and its operation is described in U.S. Pat. No.2,544,655, issued Mar. 13, 1951, to which reference may be had for a more detailed explanation of the operation of this type of meter.
By the nature of its construction, these meters are able to be run backward by a reversal of flow of fluid through them. When gas is introduced into the outlet passage and allowed to flow through the meter in a reverse direction, the index, or register also operates backward, reducing the total reading instead of increasing it. While the meter is not nearly so accurate when run backward, unscrupulous people have in the past resorted to operating the meter in the reverse direction to reduce the reading on the index, and thus avoid paying for some or all of the gas they consume. This can be accomplished in a number of ways, but the most common is simply to detach the meter from the inlet and outlet pipes and reinstall it reversed. Thus, the meter is operated in the reverse direction, and by doing this during a period when the meter is not scheduled to be read, can go undetected. While the utility company may suspect that tampering is taking place, proving the fact of tampering is difficult, and taking action on it is a sensitive matter.